Conventional IR and near IR furnaces use linear quartz-halogen-tungsten lamps as their heat source. Such furnaces may be employed for a variety of processing applications such as brazing or lid sealing, as well as for integrated circuit packaging applications.
These furnaces may achieve a minimum temperature gradient of approximately .+-.2.degree. C. across a conveyor belt up to several feet in width. Much larger gradients, however, are observed across the surface of items, or moieties, transported on the conveyor belt. The greater temperature gradient across the surface of a moiety is related to the geometry of the moiety, the emissivity and thermal conductivity of the moiety, and other physical parameters that pertain to the absorption of radiant energy by the moiety. These larger gradients may affect moiety yield in some state-of-the-art processes.
In particular, a lack of a uniform temperature across the surface of a moiety may have a negative impact on the production of multichip modules. A typical integrated circuit package is comprised of a single chip. In a multichip module several chips are placed on a substrate material that may be approximately 24".times.24" to form a single package. A multichip module typically has several layers of an organic dielectric, which may be benzocyclobutene (BCB), sandwiching metallized layers of submicron etching that provide connections for the chips placed on the module. If the organic dielectric layers are not uniformly cured the layers of the organic dielectric may delaminate, thereby affecting the reliability of the module.
Moreover, monitoring, or process control, of the curing process typically involves the use of the statistical methods at aggregate levels. These methods do not allow for individualized moiety monitoring and control, and thus limits total moiety curing yield.
Additionally, near-infrared furnaces are often not constructed to provide ultra-clean environments within the heated chambers. In some state-of-the-art processes, however, particulate contamination is a factor. Particulates in the micron or submicron range can contaminate semiconductor applications, thereby reducing part reliability and yield. Particulate contamination of the furnace atmosphere can arise from several sources. These sources include furnace insulation, friction due to a conveyor assembly or contacting movement of items within the furnace, and from particulates present in the source atmosphere.